The origin of the Dutch language
The Netherlands is a relatively small country with only 17 million inhabitants. Throughout history the Dutch have always been merchants, travelling the world and seeking business opportunities, sometimes even colonising other countries. You can find Dutch spoken in places such as Surinam, China, the Antilles, Indonesia, South-Africa, and even some small towns in Brazil.
The origin of the Dutch language has been set by linguists at about 700 AD and belongs to the Germanic language family. It has since had many influences, especially Latin.
If you intend on living in the Netherlands or are planning on a serious career in a Dutch company, you need to learn Dutch. If you are only planning to stay a short while, or will only work for international companies, you may be able to get by without. In Holland almost everyone speaks English and usually one or two other languages as well. So, getting around in Holland should be fairly easy from day one.
What's not Dutch then?
Alongside Dutch, another language called Frisian is spoken in some parts of the Netherlands. Frisian is not a dialect of Dutch but an independent West-Germanic language which has developed in parallel, albeit with similarities to and strongly influences from Dutch.